[React Testing] Test React Component Event Handlers with fireEvent from React Testing Library

The fireEvent utility in React Testing Library supports all the events that you regularly use in the web (change, click, etc.). Let’s see how we can test our change event handler with an input.

Component:

<input
        id="favorite-number"
        type="number"
        value={number}
        onChange={handleChange}
      />
      {isValid ? null : <div role="alert">The number is invalid</div>}

As we can see, the input has a 'onChange' event, and also there is a message display when the number is outside [1, 9]

Test:

import React from 'react'
// extend expect object to have methods from jest-dom
import '@testing-library/jest-dom/extend-expect'
import { render, fireEvent } from '@testing-library/react'
import { FavoriteNumber } from './favorite-number'

test('entering an invalid value shows an error message', () => {
  const { getByLabelText, getByRole } = render(<FavoriteNumber />)
  const input = getByLabelText(/favorite number/i)
  // fire a change event
  fireEvent.change(input, { target: { value: 10 } })
  expect(getByRole('alert')).toHaveTextContent(/the number is invalid/i)
})